A diagnostic method for quantitatively checking actuating elements in internal combustion engines (U.S. Pat. No. 4,794,790) is known for which however a diagnosis is only then possible when the regenerating gas flow contains so little fuel that practically no additional fuel quantity results when a regenerating gas flow is supplied via the tank-venting valve.
Accordingly, it is an object of the invention to provide an appropriate diagnostic method which permits such actuators to be checked independently of the air/fuel ratio of the regenerating flow during operation.